CN110608232B

CN110608232B - Method of manufacturing an oilless bearing with an embedded solid lubricant plug

Info

Publication number: CN110608232B
Application number: CN201811375655.1A
Authority: CN
Inventors: 崔太树
Original assignee: SGO
Current assignee: SGO
Priority date: 2018-06-15
Filing date: 2018-11-19
Publication date: 2020-12-18
Anticipated expiration: 2038-11-19
Also published as: KR101924195B1; CN110608232A; JP2019219054A; EP3581819B1; JP6641563B2; ES2862332T3; EP3581819A1

Abstract

The present invention provides a method of manufacturing an oilless bearing having an embedded solid lubricant plug, comprising the steps of: forming a hole in the brass body to receive the solid lubricant plug therein; mixing a thermally expandable and curable dry resin powder and a dry solid lubricant powder to make a dry powder mixture; filling the dry powder mixture into the hollow part of the mold; compressing the dry powder mixture to form a dry powder compact plug; tightly inserting each dry powder into each hole of the brass body; heat treating the brass body into which the dry powder compact plug is inserted, in a vacuum or inert gas heat treatment furnace at a temperature equal to or higher than that of the solidified heat expandable and curable resin, such that the dry powder compact plug within the hole is melted, expanded and sintered, and then cooled, forming a porous solid lubricant plug that is firmly adhered within the hole of the brass body; and injecting an oil into the porous solid lubricant plug.

Description

Method of manufacturing an oilless bearing with an embedded solid lubricant plug

Technical Field

The present invention relates to a method for manufacturing an oil-free bearing having an embedded solid lubricant plug (embedded solid lubricant plugs) with a solid lubricant composition ratio for improving oil injection characteristics, and more particularly, to a method for manufacturing an oil-free bearing having a solid lubricant composition ratio for improving oil injection characteristics of an embedded solid lubricant plug and simultaneously improving adhesion between a brass body and a solid lubricant plug in an oil-free bearing having an axial sliding surface in which a solid lubricant plug is embedded in a brass body.

Background

In oil-free bearings with embedded solid lubricant plugs, oil is injected into the solid lubricant plugs except when used at high temperatures where the oil can be acidified, such as around a smelting furnace in a steel plant, etc.

When friction is generated by relative movement between the opposing materials, i.e., the oilless bearing and the shaft or pin, heat is generated that causes the injected oil to flow out of the solid lubricant plug and be provided to the sliding surface. When the relative motion stops and no friction is generated, the oil is once again absorbed into the solid lubricant plug.

Sufficient oil injection is necessary, especially for opposed materials with high speed motion.

As a prior art, korean registered patent publication No. 10-0823828 discloses a manufacturing process of an oilless bearing having an embedded solid lubricant plug that is currently used.

Japanese laid-open patent application nos. 2013092222 and H06-200946 disclose a method of manufacturing an oilless bearing having an embedded solid lubricating plug of another shape.

However, the prior oilless bearing with an embedded solid lubrication plug disclosed in the related patent document has the following two problems:

the first is that the solid lubricant plug falls out of its hole, and the other is that the oil injection is not easily achieved or the oil injection volume is too small.

Generally, an oilless bearing with an embedded solid lubricant plug is manufactured by forming a mixture of carbon and alloadhesive in the shape of a plug, hardening the plug by using heat or curing agent, coating an adhesive on the surface of the solid lubricant plug, inserting the solid lubricant plug into a hole formed in a brass body, and coagulating the solid lubricant plug by using the adhesive.

That is, in the oilless bearing having the embedded solid lubricant plug, the solid lubricant plug is manufactured by mixing carbon and a liquid gum, forming a mixture having a predetermined size or a standard plug shape, and hardening the plug by a hardening agent or heat before the solid lubricant is inserted into the brass body. To assemble the solid lubricant plugs to the brass body, holes are punched in the brass body, and the surfaces of the solid lubricant plugs are covered with adhesive and inserted into the holes, which are bonded together by drying the adhesive.

Some holes are formed in the brass body at fixed intervals, and since the holes are formed so that the solid lubricant plugs covered with the adhesive are inserted, the size of the holes is always larger than the outer diameter of the solid lubricant plugs.

As a result, since the solid lubricant plug covering the adhesive is inserted into the hole formed in the brass body, when the adhesive is dried and thus the solid lubricant plug is only partially bonded with the brass body, a gap may be easily generated between the solid lubricant plug and the brass body.

Further, when heat is generated at the sliding surface during use, the adhesive layer is easily deteriorated so that the adhesive force is weakened or the bonded areas are separated, causing the solid lubricant to fall out of the hole during the operation of the machine.

Particularly in the case where an oilless bearing is used for the pin guide sleeve of the injection molding machine, if the solid lubricant plug protrudes even slightly from the hole in the brass body toward the inside of the brass body when the plug pin is outside the pin guide sleeve, the solid lubricant plug is caught by the plug pin and may be damaged or fall out of the hole when the plug pin enters the brass body and moves.

As described above, in the method of manufacturing the solid lubricant plug to conform to the predetermined standard, the hole is formed to conform to the size of the solid lubricant plug in the brass body, the adhesive is applied to the solid lubricant plug and the solid lubricant plug is inserted into the hole of the brass body, the adhesive force between the brass body and the solid lubricant plug is deteriorated, the solid lubricant plug is caused to fall out of the hole of the brass body, or to be damaged during use of the bearing.

Further, in the case where the solid lubricant plug is made by mixing carbon and liquid gum, a mixture in the shape of a plug is formed in advance, the plug is heat-hardened and then inserted into a hole of the brass body. Since the pores of most of the carbon forming the solid lubricant plugs are filled with liquid glue and the bonding has been performed by applying an adhesive to the surface of the solid lubricant plugs to be inserted into the brass body, it is difficult to inject oil therein, so that the amount of oil injection is very small.

The prior art of korean registered patent publication No. 10-0823828 relates to a method of manufacturing an oil free bearing, which comprises the steps of: rough cutting a metal such as brass into a sleeve or a sheet larger than a real size; punching a cylindrical hole through metal to manufacture a body; cutting a solid carbon core (obtained by pre-forming a plug-shaped mixture of carbon and liquid gum, and heat-hardening the plug-shaped mixture) which extends with a uniform diameter longer than the hole; coating an adhesive on the longitudinal surface of the cut carbon core; inserting the carbon core coated with the adhesive into the hole of the body; drying the body into which the carbon core is inserted to harden the binder; and finally cutting the body, into which the carbon core is inserted, to be longer than the hole, based on the designed size.

However, since the carbon core may easily fall out of the pores as described in the above-mentioned prior art, the prior art described in korean registered patent publication No. 10-0823828 proposes a method of manufacturing an oilless bearing having a tapered carbon core, which comprises the steps of: rough cutting a metal such as brass into a sleeve or a sheet larger than a real size; punching a conical hole which is narrowed from the outer surface to the sliding surface in a penetrating way to manufacture a body; mixing carbon powder and liquid glue to make the carbon paste fill the conical holes; filling the carbon paste into the tapered hole of the body to form a carbon core; hardening the carbon paste by heating the body filled with the carbon paste in a drying furnace at 300-350 ℃; and finally cutting the body with the hardening of the carbon paste based on the designed size.

The prior art described in korean registered patent publication No. 10-0823828 has an effect that the carbon core does not fall out.

However, in the prior art of Korean registered patent publication No. 10-0823828 and the prior art described in Korean registered patent publication No. 10-0823828, since the carbon core is formed by mixing carbon and a liquid gum, the porosity of the carbon is significantly reduced. Further, since the binder attempts to form an adhesive layer on the surface of the carbon core when the carbon is inserted into the body, it is difficult to inject the oil therein and the amount of oil injected is very small.

In japanese laid-open patent application No. 2013092222, a resin solid lubricant (resin molded containing graphite) is cooled to shrink by using dry ice and then inserted into the holes of the base material, thereby preventing the resin solid lubricant from falling out of the holes.

However, since the resin solid lubricant is also made by mixing liquid resin and graphite, the mixture is formed into a plug shape and the mold is heat-hardened, the porosity is greatly reduced.

Japanese laid-open patent application No. H06-200946 discloses a method for heat-hardening a solid lubricant filled in a spiral groove with wettability and fluidity.

Japanese laid-open patent application No. H06-200946 relates to a cylindrical bearing with solid lubricant embedded and fixed. The solid lubricant has wettability and fluidity, is filled in the spiral groove and the annular groove formed on the inner peripheral surface, and is composed of 5-30% by weight of solid lubricant powder as a main component, 2-15% by weight of the lubricating oil agent is absorbed and retained by the carrier, and 15-50% by weight of the synthetic resin binder.

In japanese laid-open patent application No. H06-200946, a solid lubricant having wettability and fluidity is filled in a spiral groove and an annular groove formed in a cylindrical metal base material; the metal base material is maintained in a heating furnace at 80 ℃ for 60 minutes to harden the synthetic resin binder; the metal base material is maintained in the heating furnace at 140 c for 30 minutes, additionally hardening the synthetic resin binder, and simultaneously bonding the solid lubricant containing the lubricating oil to the spiral groove and the annular groove.

As for the specific component of the solid lubricant, the solid lubricant powder may use, as a main component, a substance having a solid lubricating action by itself, which is formed by one or more selected from natural graphite, artificial graphite, natural flake graphite, kish graphite, expandable graphite, molybdenum disulfide, polytetrafluoroethylene resin, and boron nitride. As the lubricating oil agent which is liquid or pasty at room temperature, one or more selected from mineral oils (e.g., engine oil or engine oil), vegetable oils (e.g., castor oil or the like), synthetic oils (e.g., ester oils or silicone oil or the like) and greases can be used. The carrier for absorbing and retaining the lubricating oil agent may use one or more selected from hydrocarbon waxes, higher fatty acids, waxes obtained by derivatizing higher fatty acids, polyolefin resin powders, oil-based fibers, cross-bridged porous spherical particles with styrene or methacrylic acid system as a main component, and porous calcium carbonate, and the like. The synthetic resin binder may use thermosetting resins such as epoxy resins, phenol resins, polyester resins, and the like, preferably, liquid epoxy resins curable at room temperature, thermosetting liquid epoxy resins, or thermosetting epoxy resin powders, in particular.

However, the prior art described in japanese laid-open patent application No. H06-200946 loses the adhesiveness of the solid lubricant and the injection property of the lubricant (oil).

The lubricating oil agent contained in the solid lubricant has wettability and fluidity before heating, and not only inhibits the synthetic resin binder from adhering to the grooves of the metal base material during the process of hardening the synthetic resin binder, but also is mostly discharged from the solid lubricant during the heating process of the heating furnace at a temperature of 140 ℃.

Documents of the prior art

(patent document 1) Korean registered patent publication No. 10-0823828 (registration date: 2008, 4 months and 21 days)

(patent document 2) Japanese published patent application No. 2013092222 (published: 2013, 5, 16)

(patent document 3) Japanese published patent application No. H06-200946 (published date: 1994, 7, 19)

Disclosure of Invention

Technical problem to be solved

Accordingly, an object of the present invention is to solve the above-mentioned problems and to provide a method for manufacturing an oilless bearing having an embedded solid lubricant plug, which prevents generation of a gap or clearance between the solid lubricant plug embedded in a hole of a brass body and the brass body or generation of a discontinuous boundary from a source, which enables firm adhesion between the solid lubricant plug and the brass body for a long time.

It is another object of the present invention to provide a method for manufacturing an oilless bearing having an embedded solid lubricant plug that facilitates oil injection and high volume oil injection by maintaining porosity at the inner and outer surfaces of the solid lubricant plug during formation of the solid lubricant plug.

(II) technical scheme

In accordance with an embodiment of the present invention to achieve the above object, there is provided a method of manufacturing an oilless bearing having an embedded solid lubricant plug, including the steps of: forming a hole in the brass body to receive the solid lubricant plug therein; mixing a thermally expandable and curable dry resin powder and a dry solid lubricant powder, mixing the dry powders; filling the dry powder mixture into the hollow part of the mold; compressing the dry powder mixture to form a dry powder compact plug to fit into the hole in the brass body; tightly inserting each dry powder into each hole of the brass body; heat treating the brass body into which the dry powder compact plug is inserted, in a vacuum or inert gas heat treatment furnace at a temperature equal to or higher than that of the cured heat expandable and curable resin, such that the dry powder compact plug within the hole expands and sinters, and then cools to form a porous solid lubricant plug that adheres firmly within the hole of the brass body; and injecting an oil into the porous solid lubricant plug, wherein the dry powder mixture is composed of a dry solid lubricant powder having 45-60 weight percent (wt%) of crystalline flake graphite, 10-15 wt% of natural graphite, and 10-15 wt% of barium sulfate, and 20-25 wt% of a thermally expandable and curable dry resin powder.

Preferably, the heat treatment in the heat treatment furnace is performed at a temperature of 150 to 250 ℃ for 0.5 to 2 hours.

Preferably, the compressing of the dry powder mixture of the thermally expandable and curable dry resin powder and the dry solid lubricant powder is performed at a pressure of 2,000 to 5,000 kgf/kg.

Preferably, inserting the dry powder compact plug into the hole of the brass body further comprises the step of coating a thermally expandable and curable resin on a surface of the dry powder compact plug.

Preferably, the post-treatment step of removing any unnecessary area by rough cutting and sizing by final cutting is performed before the oil is injected into the porous solid lubricant plug.

Preferably, mixing the dry solid lubricant powder comprises the steps of: mixing the raw materials by mixing crystalline flake graphite, natural graphite, barium sulfate and alcohol; drying the mixed raw materials; pulverizing the dried raw material and sieving the pulverized raw material by using 50-150 mesh; and collecting the sieved raw material and remixing the collected raw material by using a mixer.

(III) advantageous effects

According to the above composition of the present invention, the solid lubricant plug is formed in the hole of the brass body by sintering the dry solid lubricant powder.

The dry powder-tightly packed mixture is inserted into the hole of the brass body, the crystalline flake graphite core is thermally expandable and curable, and the like, and expands, sinters and hardens during the heat treatment, fills the space of the hole without any gaps, and tightly adheres to the brass body.

Therefore, when the solid lubricant plug is formed in the hole of the brass body, no gap (or clearance) is generated between the brass body and the solid lubricant plug, and a firm adhesion is maintained for a long time.

Further, during the sintering process, the required oil injection amount is controlled by changing the composition ratio of the crystalline flake graphite, the natural graphite, the barium sulfate and the curable dry resin powder, which is the composition of the solid lubricant plug.

Further, the holes are widely distributed over the surface of the solid lubricant plug.

Drawings

The above and other features and advantages of the present invention will be apparent from the following detailed description of embodiments of the invention with reference to the accompanying drawings.

Fig. 1 is a cross-sectional view of a brass body having holes in accordance with an embodiment of the present invention.

Fig. 2 is a cross-sectional view illustrating a method of manufacturing a dry powder compact plug according to an embodiment of the present invention.

Fig. 3 is a cross-sectional view of a dry powder compact plug formed by the method of fig. 2.

Fig. 4 is a sectional view illustrating coating of a thermally expandable and curable liquid resin on the surface of the dry powder compact plug shown in fig. 3.

Fig. 5 is a cross-sectional view illustrating the insertion of the dry powder compact plug of fig. 4 into the brass body of fig. 1.

Fig. 6 is a sectional view illustrating a method of sintering the brass body shown in fig. 5 with the dried powder compact plug inserted therein in a heat treatment furnace.

Fig. 7 is a cross-sectional view illustrating a porous solid lubricant plug formed within a bore of a brass body.

Fig. 8 is a cross-sectional view illustrating a method of injecting oil into a porous solid lubricant plug formed in a bore of a brass body.

FIG. 9 is a perspective view of an oilless bearing having an embedded solid lubricant plug to improve oil injection characteristics in accordance with the present invention.

Fig. 10 is a graph showing the expansion rate and the compression strength according to examples each having a different composition ratio of the solid lubricant.

Fig. 11 is a graph showing the compressive strength and the expansion ratio based on the temperature of crystalline flake graphite.

Fig. 12 is a picture of crystalline flake graphite photographed by a scanning microscope in korean Testing and Research Institute.

Fig. 13 is a picture of natural graphite taken by a scanning microscope in korean test and research institute.

Fig. 14 is a picture of the powder mixture 1 (crystalline flake graphite + natural graphite + barium sulfate) photographed by a scanning microscope in korean test and research institute.

Fig. 15 is a picture of the powder mixture 2 (crystalline flake graphite + natural graphite + barium sulfate + binder) photographed by a scanning microscope in korean test and research institute.

Fig. 16 is a picture of barium sulfate taken by a scanning microscope in korean test and research institute.

Fig. 17 is a picture of the powder mixture 2 as a solid lubricant plug before heat treatment taken by a scanning microscope in korean test and research institute.

Fig. 18 is a picture of the powder mixture 2 as a solid lubricant plug after heat treatment taken by a scanning microscope in korean test and research institute.

Fig. 19 is a perspective view and a partial enlarged view of holes formed in a brass body in accordance with other embodiments of the present invention.

Detailed Description

Hereinafter, the present invention will be described more fully with reference to the accompanying drawings. For reference, the size of the composition, the width of the line, and the like shown in the drawings may be exaggerated for ease of understanding.

The terms used herein are defined by taking into account the functions of the present invention, and thus may be different according to user or operator intentions or court cases. Therefore, the definitions of the words used should be based on the overall content described in the present invention.

It will be understood that the terms "comprises," "comprising," "includes" and/or "including" when used herein, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, step operations, element components, and/or groups thereof, unless otherwise indicated herein.

This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

Thus, while embodiments of the invention are capable of various modifications and alternative forms, examples (aspects or embodiments) of the invention are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that there is no intention to limit the exemplary embodiments of this invention to the specific forms disclosed, but on the contrary, the exemplary embodiments of the invention are to cover all modifications, equivalents, and alternatives falling within the scope of the invention. As used herein, the singular forms "a", "an" and "the" include plural referents unless the context clearly dictates otherwise.

While functions and compositions are well known or known in the relevant art, further discussion will not be presented in the detailed description of the invention in order to clarify the subject matter of the present invention.

The method of manufacturing an oilless bearing having an embedded solid lubricant plug to improve oil injection characteristics according to an embodiment of the present invention will be described more fully hereinafter with reference to the accompanying drawings.

In fig. 1, a method of manufacturing an oilless bearing having an embedded solid lubricant plug according to an embodiment of the present invention includes a step of forming a hole 11 in a brass body 9 for forming a solid lubricant plug therein (see fig. 9).

The holes 11 are cylindrical and the number and size of the holes 11 may vary based on the size of the surface area of the brass body 9 or the use of an oilless bearing.

The brass body 9 may be a sleeve-type brass body as shown in the drawings or a sheet-like brass body, which is thin in length and width compared to the lower thickness, although not shown.

After the dry powder compact plug 3 (see fig. 5) obtained by high pressure compression is inserted into the hole 11, the dry powder is sintered in a heat treatment furnace, so that the solid lubricant plug 7 according to the invention is formed and at the same time adheres to the hole 11 of the brass body 9.

To this end, in fig. 2 and 3, the manufacturing method of the oilless bearing with the embedded solid lubricant plug further includes a step of mixing the thermally expandable and curable dry resin powder and the dry solid lubricant powder, and a step of forming the dry powder compact plug 3 by compressing the dry powder mixture 1 of the thermally expandable and curable dry resin powder and the dry solid lubricant powder at a high pressure equal to or higher than 1,000 kgf/to conform to the hole 11 of the brass body 9.

Preferably, the dry powder mixture 1 of the thermally expandable and curable dry resin powder and the dry solid lubricant powder is compressed at a high pressure of 2,000 to 5,000 kgf/g.

The most preferred thermally expandable and curable dry resin for use in the present invention is a phenolic resin. The resin expands 3-5% in volume during the thermal hardening process.

Graphite, carbon, molybdenum disulfide (MoS2), or tungsten disulfide (WS2) may be used as the solid lubricant.

In particular, it is preferable to select crystalline flake graphite or artificial carbon having thermal expansion characteristics as the solid lubricant plug.

It is understood that the crystalline flake graphite or the artificial carbon expands 15 to 22% by heating to become a solid. After the solid lubricant plug is formed by heating using the expansion rate of the crystalline flake graphite, the solid lubricant is inserted into the hole 11 of the brass body 9 and expanded by heating.

Further, to form the dry powder mixture 1 of the thermally expandable and curable dry resin powder and the dry solid lubricant powder into a plug shape, the dry powder mixture 1 is filled into the hollow 107 of the die 105 and then compressed by the punch press 101 having the punch 103 to form the dry powder compact plug 3.

The resulting dry powder compact plugs 3 are inserted into the holes 11 of the brass body 9, respectively.

As shown in fig. 4, preferably a liquid thermally expandable and curable resin 5 is also applied to the surface of the dry powder compacted plug 3.

The reason is because if the dry powder compact plug 3 is hit before sintering and hardening, the inserted dry powder compact plug 3 may be broken or fall out of the hole 11 in the course of moving the brass body 9 to the heat treatment furnace.

In fig. 6, the manufacturing method of the oilless bearing with the embedded solid lubricant plug further includes the step of forming the porous solid lubricant plug 7 firmly fixed in the hole 11 of the brass body 9 by heat-treating the brass body 9 in which the dry powder compact plug 3 is inserted in a vacuum heat-treating furnace 109 or a heat-treating furnace of an inert gas at a temperature equal to or higher than that of curing the heat-expandable and curable resin, so that the dry powder compact plug in the hole 11 is expanded and sintered, and then cooled.

The heating temperature is 150-250 ℃, preferably 180-220 ℃.

When the solid lubricant plug 7 is formed in the above manner, the porosity is increased to 10 to 20%.

In fig. 8, the manufacturing method of the oilless bearing with the embedded solid lubricant plug further includes a step of injecting oil into the solid lubricant plug 7 by immersing the brass body 9, in which the porous solid lubricant plug 7 is formed in the hole 11, into the oil tank 113.

In fig. 9, the oilless bearing with the embedded solid lubricant plug filled with oil is obtained by a post-processing step.

In the post-processing step, any unwanted parts are removed by rough cutting, and the adjustment of size is made by final cutting.

Oil injection may be performed after the post-treatment step.

In the method of manufacturing an oilless bearing having an embedded solid lubricant plug according to the present invention, the solid lubricant plug expands and hardens during the heat treatment process to firmly fill the hole 11 of the brass body 9, without a gap and firmly adhere to the brass body 9. Therefore, there is no gap between the brass body 9 and the solid lubricant plug, and the solid lubricant plug does not separate from the brass body 9 even if the oilless bearing is used for a long time.

Further, the oil is easily injected into the holes formed when the solid lubricant plug 7 expands by heating, and the injection amount of the oil is controlled by controlling the composition ratio of the crystalline flake graphite, which has a relatively large degree of contribution to the expansion of the solid lubricant plug in the composition.

The composition of the thermally expandable and curable dry resin powder and dry solid lubricant powder for the solid lubricant plug will be described below.

Fig. 10 is a graph showing expansion rate and compression strength according to examples of composition ratios of respective plugs with different solid lubricants, and fig. 11 is a graph showing compression strength and expansion rate based on the temperature of crystalline flake graphite.

Fig. 12 is a picture of crystalline flake graphite, fig. 13 is a picture of natural graphite, fig. 14 is a picture of powder mixture 1 (crystalline flake graphite + natural graphite + barium sulfate), fig. 15 is a picture of powder mixture 2 (crystalline flake graphite + natural graphite + barium sulfate + binder), fig. 16 is a picture of barium sulfate, fig. 17 is a picture of powder mixture 2 as a solid lubricant plug before heat treatment, and fig. 18 is a picture of powder mixture 2 as a solid lubricant plug after heat treatment, which are all photographed by a scanning microscope in korean test and research institute.

In an embodiment of the present invention, the dry solid lubricant powder of the dry powder mixture is composed of 45 to 60 weight percent of crystalline flake graphite, 10 to 15 weight percent of natural graphite and 10 to 15 weight percent of barium sulfate, and the thermally expandable and curable dry resin powder of the dry powder mixture is composed of 20 to 25 weight percent of phenolic dry resin powder, which is heated in an inert gas heat treatment furnace at 150 to 250 ℃ for 0.5 to 2 hours.

Fig. 11 is a graph showing the compressive strength and the expansion ratio based on the temperature of crystalline flake graphite, and table 1 shows the expansion ratio according to the temperature of crystalline flake graphite.

TABLE 1

Hardening temperature (. degree.C.)	100℃	150℃	200℃	250℃
					Expansion ratio	15.7％	19.4％	19.0％	19.2％

Expansion ratio (volume after heating-volume before heating)/volume before heating

Since the ratio of oil injection is the corresponding expansion ratio, it is preferable to control the expansion ratio to obtain the required oil injection amount.

The crystalline flake graphite is expanded by heating to be sintered. As the temperature increases, the expansion rate of the crystalline flake graphite increases. However, at 150 ℃ or more, the expansion ratio of the crystalline flake graphite is about 19%, showing no great change. At 150 ℃ or more, the compressive strength is 170 kgf/or more, which is greater than the strength value required as a lubricant for oilless bearings, 150 kgf/.

The natural graphite has a lubricating function with a rotating body or an object generating sliding. Although it is preferable to increase the composition ratio of natural graphite in terms of lubrication effect, the composition ratio of natural graphite is preferably 10 to 15 weight percent because the expansibility is considered in the present invention to insert the lubricant in the form of a plug to be fixed to the brass body 9 by heating.

When barium sulfate is mixed with a thermally expandable and curable resin and alcohol, barium sulfate tends to aggregate together.

Barium sulfate, which binds the mixture together when mixed with crystalline flake graphite powder, natural graphite powder, thermally expandable and curable resin as a binder, and alcohol, allows the mixture to be smoothly transformed to form a solid lubricant plug, and has holes in the powder mixture when the dry powder is tightly plugged to fill the holes to form a solid lubricant plug. The barium sulfate improves the wear resistance after sintering. The best effect is obtained when 10-15 wt% of barium sulfate is contained in the powder mixture.

The thermally expandable and curable resin acts as a binder to bind the solid lubricant plug and prevent the various components from spreading.

The thermally expandable and curable resin as the binder uses a mixture of the binder and the hardener. The heat expandable and curable resin as the binder has 90 to 97 parts by weight of the binder and 3 to 10 parts by weight of the hardener per 100 parts by weight.

The step of mixing the dry solid lubricant powder further comprises the steps of: mixing raw materials of crystalline flake graphite, natural graphite, barium sulfate, alcohol and a thermally expandable and curable resin as a binder; drying the mixed raw materials; pulverizing the dried raw material and sieving the pulverized raw material with 50-150 mesh; the screened feedstock is then collected and the collected feedstock is remixed using a mixer.

When the step of mixing the dry solid lubricant powder is sequentially performed, it is affected that the distribution ratio and the particle size of each composition of the dry solid lubricant powder are uniform.

Fig. 14 is a picture of a powder mixture 1 (crystalline flake graphite + natural graphite + barium sulfate), the powder mixture 1 not containing alcohol and a thermally expandable and curable resin as a binder. In this case, the particles are not bonded together. However, as shown in fig. 15 for powder mixture 2 (crystalline flake graphite + natural graphite + barium sulfate + binder), the particles were bonded together. This confirms that the barium sulfate is aggregated together.

Fig. 17 is a picture of the powder mixture 2 as a solid lubricant plug before heat treatment, and fig. 18 is a picture of the powder mixture 2 as a solid lubricant plug after heat treatment.

As shown in fig. 17, the pores between the particles are narrow before the heat treatment, however, as shown in fig. 18, it is confirmed that the size of the particles is increased during the heating and sintering process and the pores between the particles are enlarged, and the oil required for lubrication is injected into the pores.

The invention will be explained on the basis of the following examples.

As demonstrated in table 1 and fig. 11, the crystalline flake graphite expands when heated and sintered. The expansion ratio of the crystalline flake graphite exceeds 19% at a temperature of 150 ℃ or more, but it does not change much. It is therefore preferable that the heating temperature is 150 ℃ or more. Since heating to 250 ℃ or higher does not have a more desirable effect on the thermally expandable and curable resin, the heating temperature is preferably 150 to 250 ℃.

Table 2 and fig. 10 show experimental results obtained by heating at 200 c for 1 hour while varying the composition ratio of the crystalline flake graphite and the natural graphite when barium sulfate is mixed at 13 weight percent and the thermally expandable and curable dry resin powder is mixed at 22 weight percent.

TABLE 2

As shown in table 2 and fig. 10, in example 1, the powder mixture consisting of 20 weight percent of crystalline flake graphite, 45 weight percent of natural graphite, 13 weight percent of barium sulfate, and 22 weight percent of thermally expandable and curable dry resin powder had an expansion ratio of 5.5% and a compressive strength of 204.2 kgf/. This confirms that the expansion ratio does not satisfy 15% as expected.

In example 2, a powder mixture consisting of 30 weight percent of crystalline flake graphite, 35 weight percent of natural graphite, 13 weight percent of barium sulfate, and 22 weight percent of thermally expandable and curable dry resin powder, after heating and sintering, had an expansion ratio of 9.9% and a compressive strength of 321.1 kgf/. This confirms that the expansion ratio does not satisfy 15% as expected.

In example 3, the powder mixture consisting of 40 weight percent of crystalline flake graphite, 25 weight percent of natural graphite, 13 weight percent of barium sulfate, and 22 weight percent of heat-expandable and curable dry resin powder, after heating and sintering, had an expansion ratio of 13.4% and a compressive strength of 355.6kgf/. this confirmed that the expansion ratio did not satisfy 15% as expected.

In example 4, the powder mixture consisting of 50 weight percent of crystalline flake graphite, 15 weight percent of natural graphite, 13 weight percent of barium sulfate, and 22 weight percent of heat-expandable and curable dry resin powder, after heating and sintering, had an expansion ratio of 15.2% and a compressive strength of 311.8kgf/. this confirmed that the expansion ratio satisfied 15% as expected.

In example 5, the powder mixture consisting of 52 weight percent of crystalline flake graphite, 13 weight percent of natural graphite, 13 weight percent of barium sulfate, and 22 weight percent of thermally expandable and curable dry resin powder, after heating and sintering, had an expansion rate of 16.7% and a compressive strength of 290.4kgf/. this confirmed that the expansion rate satisfied 15% as expected.

In example 6, the powder mixture consisting of 60 weight percent of crystalline flake graphite, 5 weight percent of natural graphite, 13 weight percent of barium sulfate, and 22 weight percent of thermally expandable and curable dry resin powder, after heating and sintering, had an expansion rate of 18.9% and a compressive strength of 247.2kgf/. this confirmed that the expansion rate satisfied 15% as expected.

From examples 1 to 6, it was confirmed that the preferable composition ratio of the crystalline flake graphite satisfying the expansion ratio and the compression ratio was 45 to 60% by weight.

It was also confirmed that the oil injection amount was controlled by controlling the composition ratio of the crystalline flake graphite, which is a composition component having a relatively large degree of contribution to the expansion of the solid lubricant plug.

For oil-free bearings with voids for oil injection, the expansion rate is expected to be over 15%, and the strength value for the lubricant plug is expected to be 150 kgf/or higher.

According to other embodiments of the invention, the hole for receiving the solid lubricant plug is formed in the brass body by the following description:

as previously described, a bore hole 11 receiving a plug of solid lubricant is formed in the brass body 9. In this embodiment, the hole prevents the solid lubricant plug inserted into the hole 11 from falling out of the hole 11.

Fig. 19 is a perspective view and a partial enlarged view of a hole formed in a brass body.

As shown in fig. 19, the hole 11 in the brass body 9 which receives the solid lubricant plug contains a protrusion on the inner circumferential surface. Each projection is configured to be inclined towards the centre line of the hole 9.

The solid lubricant plug inserted into the hole 11 of the brass body 9 has the above-described structure that expands by heating, and the expanded solid lubricant plug is firmly adhered by the protrusion, thereby preventing it from falling out of the hole.

The protrusion may optionally have a wavy shape, a threaded shape, or a cylindrical shape, as desired.

In the composition of the dry powder compact plug inserted into the hole of the brass body, the dry resin powder, which is thermally expandable and curable, melts, expands, sinters and hardens during the heat treatment. The invention has the effect that the plug filled in the hole space has no gap and is tightly adhered to the brass body.

Further, when the solid lubricant plug is formed in the hole of the brass body, no gap occurs between the brass body and the solid lubricant plug, and the firm adhesion is maintained for a long time.

The voids created between the particles of the thermally expandable and curable dry resin powder during the sintering process maximize porosity because the dry solid lubricant powder does not block the voids and the voids are widely distributed over the surface of the solid lubricant plug. Therefore, the present invention has a remarkable function and effect in making it easy to inject oil and increasing the amount of oil injected.

While the invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the following claims. The scope of the claims is, therefore, to be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.

Claims

1. A method of manufacturing an oilless bearing having an embedded solid lubricant plug, comprising the steps of:

forming a bore (11) in the brass body (9) to receive a plug of solid lubricant therein;

mixing a thermally expandable and curable dry resin powder and a dry solid lubricant powder to produce a dry powder mixture (1);

filling the dry powder mixture (1) into the hollow (107) of a mold (105);

compressing the dry powder mixture (1) to form a dry powder compact plug (3) to fit into the hole (11) of the brass body (9);

inserting each dry powder compact plug (3) into each hole (11) of the brass body (9);

heat-treating the brass body (9) in which the dry powder compact plug (3) is inserted, in a heat-treating furnace in vacuum or in an inert gas, at a temperature equal to or higher than the temperature at which the thermally expandable and curable resin is cured, so that the dry powder compact plug (3) inside the hole (11) melts, expands and sinters, and then cools, forming a porous solid lubricant plug (7) that adheres firmly inside the hole (11) of the brass body (9); and

injecting an oil into the porous solid lubricant plug (7);

wherein the dry powder mixture (1) is composed of a dry solid lubricant powder having 45 to 60 weight percent of crystalline flake graphite, 10 to 15 weight percent of natural graphite and 10 to 15 weight percent of barium sulfate, and 20 to 25 weight percent of thermally expandable and curable dry resin powder.

2. A method of manufacturing an oilless bearing with an embedded solid lubricant plug as claimed in claim 1,

the heat treatment in the inert gas heat treatment furnace is carried out at a temperature of 150 to 250 ℃ for 0.5 to 2 hours.

3. A method of manufacturing an oilless bearing with an embedded solid lubricant plug as claimed in claim 2,

the dry powder mixture (1) for compressing the thermally expandable and curable dry resin powder and the dry solid lubricant powder is in the range of 2,000 to 5,000kgf/cm²Under pressure of (c).

4. A method of manufacturing an oilless bearing with an embedded solid lubricant plug as claimed in claim 3,

inserting the dry powder compact plug (3) into the hole (11) of the brass body (9) further comprises the step of applying a thermally expandable and curable resin to the surface of the dry powder compact plug (3).

5. A method of manufacturing an oilless bearing with an embedded solid lubricant plug as claimed in claim 4,

also included is a post-treatment step of removing any unnecessary area by rough cutting and sizing by final cutting, before the oil is injected into the porous solid lubricant plug (7).

6. A method of manufacturing an oilless bearing with an embedded solid lubricant plug as claimed in claim 1, wherein mixing dry solid lubricant powder comprises the steps of:

mixing the raw materials by mixing crystalline flake graphite, natural graphite, barium sulfate and alcohol;

drying the mixed raw materials;

pulverizing the dried raw material and sieving the pulverized raw material by using 50-150 mesh; and

collecting the sieved feedstock and remixing the collected feedstock by using a mixer.